Field of the Invention
The invention concerns a semiconductor sensor component with a semiconductor body in which both a sensor and an evaluation circuit are formed in an integrated manner and are protected by an encapsulation.
It is known that semiconductor sensors must be protected against the effects of process and environment. At the same time, it is necessary that the semiconductor sensor remains accessible for the medium to be measured. For example, the configuration for the semiconductor pressure sensor must allow the actual semiconductor pressure sensor to be coupled to the pressure to be measured. In other words, a changing pressure must be able to exert an effect on the surface of the semiconductor sensor. The same applies, for example, for temperature sensors, humidity sensors, etc. In this connection care must be taken that the protective case of the semiconductor sensor introduces the minimum possible delay in performing the measurement.
In an existing semiconductor pressure sensor configuration the semiconductor body of the actual semiconductor sensor is accommodated on a circuit board in an inner case equipped with a membrane, which case is provided together with an evaluation logic circuit in an outer case. Access of the measuring medium, i.e. mostly air or gas, to the inner case proceeds over a silicone membrane of the outer case. A construction of this kind leads inevitably to relatively large modules since the semiconductor sensor and the evaluation logic circuit are provided in different semiconductor bodies.
Semiconductor sensor configurations in which the actual semiconductor sensor and the evaluation logic circuit are combined in a single semiconductor body must be accommodated in a case that is open on one side. Up to now, after a semiconductor body of this kind has been bonded in the case open on one side, the semiconductor body is covered with silicone gel or a similar material and embedded. It has been found, however, that this kind of covering material does not provide adequate mechanical protection for the semiconductor body and that, also, its surface is adhesive to a certain extent that is a hindrance in practical applications. Further disadvantages are the danger that mechanical influences might destroy the semiconductor body and the effect of particles that settle on the surface of the semiconductor sensor configuration and can influence the characteristic curve of the sensor.
U.S. Pat. No. 4,732,042, for example, describes a semiconductor pressure sensor configuration in which the semiconductor is embedded in silicone rubber inside a case which is provided with a membrane on one side. In this semiconductor sensor configuration the underside of the semiconductor body is freely accessible through a hole in the case so that here there exists the danger of mechanical damage. This semiconductor sensor configuration also has no evaluation electronics integrated in the semiconductor body.
Published, European Patent Application EP 0 286 867 A describes a semiconductor pressure sensor configuration in which the semiconductor body is fixed to a ribbon cable and covered with a soft plastic synthetic material. The soft plastic synthetic material is placed inside a case with an opening so that the pressure is transferred to the semiconductor body over the soft plastic synthetic material. Here too, it is possible for the semiconductor body to incur damage because the soft plastic synthetic material does not always offer reliable protection against strong mechanical effects.
The technique is also known from Published, Non-Prosecuted German Patent Application DE 44 36 485 A, of accommodating silicon strain gages inside a case in a gel-based medium in a device for determining acceleration. The gel-based medium is relatively soft so that there is no certain guarantee that the silicon strain gages are protected against mechanical effects.
From "Habekotte E. et al., in: Elektronik 1/5.1.1990, p. 80-87" and "Kayal H. A., Rauch N. in: Elektronik 9/29.4.1988, p. 112-117" semiconductor sensor devices are known in which the sensor and the evaluation logic circuit are integrated together in the semiconductor body. As a result both manufacturing costs and the dimensions of the component are reduced.
From Published, Non-Prosecuted German Patent Application DE 41 33 061 an earlier type of pressure sensor is known in which a porous plate in the outer case is located around a measuring element. The outer case protects the measuring element from direct contact with liquids. The porous plate consists of PTFE and although it prevents the passage of liquid, it allows gases through which can attack the measuring element.
U.S. Pat. No. 5,436,491 shows another pressure sensor with an outer case. The case consists of steel or a similar material. It has an upwards facing open area which is closed with a diaphragm of metal. The semiconductor pressure unit is located inside the case on a base made of glass or a similar material.
A pressure sensor with a case consisting of a lower and an upper partial case is described in U.S. Pat. No. 4,914,954. The pressure sensor is located inside the combined case; the case is closed by a labyrinth.
Finally, a pressure sensor in an open case is known from Published, Non-Prosecuted German Patent Application DE 44 13 274 A. By using a membrane the case is covered extensively and closed. This configuration also does not always provide reliable protection of the pressure sensor against strong mechanical effects.